This disclosure relates in general to content delivery and, more specifically, but not by way of limitation, to content delivery under load.
Content originators provide content objects to recipients over the Internet. The Internet is an amalgamation of various networks who pass each other's network traffic such that recipients can receive their content objects. The various networks can be divided into Tier 1 and terminal networks. All Tier 1 networks are full-route networks such that any point on the Internet can be reached by the Tier 1 network by using terminal networks and other full-route networks. Each recipient has Internet service from a terminal network, and content originators may use a combination of Tier 1 and terminal networks to deliver their content objects. The various networks, content originators and recipients pay in some way for delivering content objects using Tier 1 networks.
A content delivery network (CDN) is used by many content originators to deliver content more efficiently. The CDN may host, mirror or cache the content as well as deliver it to a requesting party. A web site or origin server is linked to the CDN such that some or all content can be sourced from the CDN rather than the content originator directly. CDNs also use Tier 1 networks and may have peering relationships with terminal networks. This process of fulfilling a link through a CDN is usually transparent to the recipient.
Today, there are about 10-15 Tier 1 networks worldwide. Some can pass 50-150 GB/min. to various destinations on the Internet. To accomplish this, Tier 1 networks pass content objects to terminal networks and peer with other Tier 1 networks. Peer Tier 1 networks agree to pass content objects from other Tier 1 networks destined to their terminal networks without cost. Tier 1 networks generally charge content providers and terminal networks for passing content objects such that peering relationships are generally avoided in these circumstances.
Peered Tier 1 networks agree to pass each other traffic only when the terminal network is not connected to the Tier 1 network receiving the traffic initially, but the other peered Tier 1 network has a connection to that terminal network. If a Tier 1 network receives a content object destined for a terminal network not directly connected to the Tier 1 network, it is passed to a peer Tier 1 network with a connection to that terminal network under the peering agreement.
Where a particular Tier 1 network has a connection to a terminal network, a content object destined for that terminal network cannot be passed to a peer Tier 1 network who may also have a connection to the terminal network. If the interconnect to the terminal network is overwhelmed, the content object may be lost. Interconnects between Tier 1 peers and terminal networks are expensive and tend to be over-built to accommodate worst-case demand.
Single casting of large events can be difficult for CDNs or Tier 1 networks to deliver effectively. Large events require content objects (e.g., files or streams) to tens of thousands of recipients in a short period of time. Egress from the CDN and/or Tier 1 networks can be overwhelmed by these large events. These egress points have finite bandwidth that serve as a bottleneck for large events. To avoid these bottlenecks, CDNs and Tier 1 networks overbuild their egress points in anticipation of the loading. In some cases today, large events cannot be served by any CDN or Tier 1 network without overloading parts of their networks. For example, a news site reporting a major and unexpected news event can find that their delivery system cannot keep up with a sudden spike in demand.
In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.